So pretty much my wife is a sexy 40DD ....
... so be happy with that!
There is no sure way to enlarge breasts with the exception of implants.
Sometimes a gain in weight does lead to larger breasts, sometime not.
Pills and creams do not help at all. Suction pumping doesn't help afaik.
So you only have three different choices:
leave her and look for a woman you like more.
Or accept her as she is and be happy with what she's got (and she's got 40DD)
Or convince her to get implants.
The second way is the best, imo.